Buick 455's weigh less than the rest(about the same as your 327), make tons of torque, best bang for the buck!
Olds for 455 don't rev to high, again tons of torque, lots jet boats and performance parts available.
Olds 403, uses 350 Olds intake, big or small block heads, breathe pretty good, they put the Smokey & the Bandit TA's on the map. Lower compression means pump gas friendly.
Pontiac 400 put the GTO on the map, tons of parts, good all around, avoid big compression or low gears, they work better on other brands.
Pontiac 455 once again, we all heard of the Super Duty, not they make cranks to turn 400's into 455's(sorta like the 383 SBC deal).
The Buick 400 is few and far between, and I am a Buick guy.
Words to live buy: There is no displacement for cubic inches!
Go as big as you can, it makes making more torque and horsepower easier.
350 Turbo will work, change the rear end gear first, to take some of the load off of the transmission go to a 3.42, 3.73, or 4.10...you're not putting a bigger motor in for gas milage right!?! (you could score these from an S-10 at a salvage)
The 350TH will need a good converter to work with that rough idle cam you want, call and get tech advice each motor will want a little different stall. You'll need a Corvette sprag race and a good shift kit. Get a cooler trans too. The Gil Younger kits come with governer springs to tune the up-shifts. Use Type F fluid.
For the 455 Buick, look to a Buick specialty source like Poston or T/A for motor mounts.
